Question

What is the approximate radius of the disc if the area is 78.5 square inches?

Answer 1

$\bf \textit{area of a circle}\\\\ A=\pi r^2~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ A=78.5 \end{cases}\implies 78.5=\pi r^2\implies \cfrac{78.5}{\pi }=r^2 \\\\\\ \sqrt{\cfrac{78.5}{\pi }}=r\implies 4.99873244587\approx r$

Answer 2

78.5 = 3.14 * r^2

r^2 = 78.5 / 3.14 = 25

r = radius = 5 answer